Bumped the d2to1 version requirement.  Also modified setup.py to run each 'setup.py install' in its own process, which ends up working better when, for example, an older version of d2to1 or stsci.distutils is being replaced.
Bumped the d2to1 version requirement.  Also modified setup.py to run each 'setup.py install' in its own process, which ends up working better when, for example, an older version of d2to1 or stsci.distutils is being replaced.

git-svn-id: 6d9763a5a770351123389058c013888add577529@13242 fe389314-cf27-0410-b35b-8c050e845b92

spacetelescope/stsci.tools